1. Field of the Invention
This invention relates to hubs upon which wheels are mounted for rotation and, more particularly, to structure for mounting a hub to a support therefor.
2. Background Art
There are many environments in which wheel-carrying hubs are required to be rigidly mounted upon a supporting frame.-One such environment is in the agricultural industry. In some agricultural equipment, a large number of soil working implements/wheels are mounted upon a frame to be simultaneously drawn through a field by a towing vehicle. One such style of implement is currently being sold by the assignee herein under the trademark TRASHWHEEL.TM..
The TRASHWHEEL.TM. implements are mounted upon a frame to rotate about transverse axes relative to the frame. Rotation is imparted to the TRASHWHEEL.TM. implements by the soil through which they are drawn. The plane of rotation of each of the TRASHWHEEL.TM. implements is non-parallel to the direction of travel of the towing vehicle. This allows the TRASHWHEEL.TM. implements to be arranged in meshing pairs that work the soil with a scissors action.
As a result of this mounting arrangement, there is a tremendous force exerted on the supporting hubs for the wheels/implements, tending to rotate the fixed portion of the hubs relative to the frame to which it attaches. Consequently, designers of such equipment must engineer the hub mounting structure to both prevent rotation of the fixed hub portion relative to the frame and separation of the fixed hub portion from the frame.
One known mounting structure requires a thick plate on the frame and uses a bolt to secure the fixed hub part to the plate. To rigidify the connection between the fixed hub part and plate, the fixed hub part is provided with a boss that extends fully through the plate. The surface bounding the plate bore and boss outer surface are keyed to prevent relative rotation between the fixed hub part and plate. A bolt is directed inside out into the fixed hub part to maintain the boss within the plate bore.
The plate bore and boss outer surface can have any non-circular shape to key the boss in the plate bore. For example, one or more flats can be provided on the boss to make this keyed connection. The boss surface could be, for example, V-shaped, rectangular, or the like.
The difficulty with creating a non-circular bore is that the bore cannot be drilled. Instead, the non-circular bore is typically formed by a stamping process.
The stamping process has some inherent drawbacks. First of all, it is a more expensive process to perform than drilling. Secondly, stamping places a restriction on the permissible thickness of the plate. For example, it is not practical to stamp plate material as thick as 1/2 inch. Consequently, the need to stamp the plate builds in an inherent limitation on the permissible plate thickness. Whereas a 1/2 inch thick frame plate may be desirable in the agricultural environment, it is not possible to use such a thick plate to mount a hub using conventional techniques.
A further problem with the conventional stamping operation is that a relatively large effective diameter bore and boss are required. Since the outer surface of the boss is responsible for preventing rotation of the fixed hub part relative to the frame, the effective diameter of this surface must be relatively large to prevent stripping of the outer surface or shearing of the boss. As a consequence, the large bore in the plate may significantly weaken the plate. This problem is aggravated by the fact that the plate thickness is limited if the stamping process is required. Also, in the agricultural environment, it is desirable to be able to mount the hub selectively in a plurality of different positions on the plate, thereby requiring multiple bores. The multiple bores further weaken the frame plate.